Abstract
In this work, CuIn1 - x Ga x Se2 (CIGS) thin films were prepared by nanosecond (ns)- and femtosecond (fs)-pulsed laser deposition (PLD) processes. Different film growth mechanisms were discussed in perspective of the laser-produced plasmas and crystal structures. The fs-PLD has successfully improved the inherent flaws, Cu2 - x Se, and air voids ubiquitously observed in ns-PLD-derived CIGS thin films. Moreover, the prominent antireflection and excellent crystalline structures were obtained in the fs-PLD-derived CIGS thin films. The absorption spectra suggest the divergence in energy levels of radiative defects brought by the inhomogeneous distribution of elements in the fs-PLD CIGS, which has also been supported by comparing photoluminescence (PL) spectra of ns- and fs-PLD CIGS thin films at 15 K. Finally, the superior carrier transport properties in fs-PLD CIGS were confirmed by fs pump-probe spectroscopy and four-probe measurements. The present results indicate a promising way for preparing high-quality CIGS thin films via fs-PLD.
Highlights
CuIn1 − xGaxSe2 (CIGS) has been extensively regarded as the most favorable absorber layer for thin film photovoltaic devices
The residual heat remaining on the target due to pulse duration difference was found to result in drastically different appearance of the laser-produced plasmas; it led to vastly different film growth mechanisms and eventual film microstructures
The CIGS thin film prepared by fs-pulsed laser deposition (PLD), as compared to that obtained by the ns-PLD process, exhibits much better film quality and superior carrier transport properties, primarily due to the removal of Cu2 − xSe and air voids
Summary
CuIn1 − xGaxSe2 (CIGS) has been extensively regarded as the most favorable absorber layer for thin film photovoltaic devices. The absorber layers for high-performance CIGSbased solar cells are usually prepared by vacuum processes (such as co-evaporation or sputtering). Pulsed laser deposition (PLD) is an alternative way that possesses the advantages of simple usage and good transfer of stoichiometry of target composition without post-selenization [4,5]. All of these advantages are beneficial to obtain high-quality and reproducible CIGS thin films at low cost and are suitable for investigating the underlying physical mechanisms that limit the efficiency
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